1. Field of the Invention
The present invention relates to a radio tag reading apparatus for reading data from a plurality of radio tags.
2. Description of the Related Art
A radio tag reading apparatus has an interrogator and an antenna connected to the interrogator. The interrogator allows output power to be generated as an electromagnetic wave from the antenna to radio tags set opposite and near to the antenna. The radio tag is of a batteryless type and, upon receipt of the electromagnetic wave from the antenna, obtains drive power. The radio tag thus obtaining the electric power sends data to the interrogator.
For the radio tag to operate upon receipt of the electromagnetic wave, it is necessary that the radio tag receive electric power of a predetermined level. However, there is a problem that the reception power falls if the distance between the radio tag and the antenna of the radio tag reading apparatus (hereinafter called the space-apart distance) becomes large. There is also a problem that, if a plurality of radio tags are overlappingly arranged even in the case where the space-apart distance becomes shorter, the reception power falls at the individual radio tags.
In a structure of JPN PAT APPLN KOKAI PUBLICATION No. 2003-283364, a plurality of radio tags are arranged in an opposed relation to an antenna connected to the interrogator and, in order to increase the reception power of the individual radio tags, a radio wave reflection plate is arranged behind the respective radio tags, in which case it has a reflection surface including a circular curve or a portion of a similar curve. By doing so, a signal which is transmitted from the antenna is reflected on the radio wave reflection plate to allow it to be received by the individual radio tags.